import type { Identifier, Unsubscribe } from 'dnd-core'

export interface XYCoord {
  x: number
  y: number
}

export interface HandlerManager {
  receiveHandlerId: (handlerId: Identifier | null) => void
  getHandlerId: () => Identifier | null
}

export interface DragSourceMonitor<DragObject = unknown, DropResult = unknown>
  extends HandlerManager,
    MonitorEventEmitter {
  /**
   * Returns true if no drag operation is in progress, and the owner's canDrag() returns true or is not defined.
   */
  canDrag(): boolean

  /**
   *  Returns true if a drag operation is in progress, and either the owner initiated the drag, or its isDragging() is defined and returns true.
   */
  isDragging(): boolean

  /**
   * Returns a string or a symbol identifying the type of the current dragged item. Returns null if no item is being dragged.
   */
  getItemType(): Identifier | null

  /**
   * Returns a plain object representing the currently dragged item. Every drag source must specify it by returning an object from its beginDrag() method.
   * Returns null if no item is being dragged.
   */
  getItem<T = DragObject>(): T

  /**
   * Returns a plain object representing the last recorded drop result. The drop targets may optionally specify it by returning an object from their
   * drop() methods. When a chain of drop() is dispatched for the nested targets, bottom up, any parent that explicitly returns its own result from drop()
   * overrides the child drop result previously set by the child. Returns null if called outside endDrag().
   */
  getDropResult<T = DropResult>(): T | null

  /**
   *  Returns true if some drop target has handled the drop event, false otherwise. Even if a target did not return a drop result, didDrop() returns true.
   * Use it inside endDrag() to test whether any drop target has handled the drop. Returns false if called outside endDrag().
   */
  didDrop(): boolean

  /**
   * Returns the { x, y } client offset of the pointer at the time when the current drag operation has started. Returns null if no item is being dragged.
   */
  getInitialClientOffset(): XYCoord | null

  /**
   * Returns the { x, y } client offset of the drag source component's root DOM node at the time when the current drag operation has started.
   * Returns null if no item is being dragged.
   */
  getInitialSourceClientOffset(): XYCoord | null

  /**
   * Returns the last recorded { x, y } client offset of the pointer while a drag operation is in progress. Returns null if no item is being dragged.
   */
  getClientOffset(): XYCoord | null

  /**
   * Returns the { x, y } difference between the last recorded client offset of the pointer and the client offset when the current drag operation has started.
   * Returns null if no item is being dragged.
   */
  getDifferenceFromInitialOffset(): XYCoord | null

  /**
   * Returns the projected { x, y } client offset of the drag source component's root DOM node, based on its position at the time when the current drag operation has
   * started, and the movement difference. Returns null if no item is being dragged.
   */
  getSourceClientOffset(): XYCoord | null

  /**
   * Returns the ids of the potential drop targets.
   */
  getTargetIds(): Identifier[]
}

export interface MonitorEventEmitter {
  subscribeToStateChange(
    fn: () => void,
    options?: { handlerIds?: Identifier[] }
  ): Unsubscribe
}

export interface DropTargetMonitor<DragObject = unknown, DropResult = unknown>
  extends HandlerManager,
    MonitorEventEmitter {
  /**
   * Returns true if there is a drag operation in progress, and the owner's canDrop() returns true or is not defined.
   */
  canDrop(): boolean

  /**
   * Returns true if there is a drag operation in progress, and the pointer is currently hovering over the owner.
   * You may optionally pass { shallow: true } to strictly check whether only the owner is being hovered, as opposed
   * to a nested target.
   */
  isOver(options?: { shallow?: boolean }): boolean

  /**
   * Returns a string or a symbol identifying the type of the current dragged item. Returns null if no item is being dragged.
   */
  getItemType(): Identifier | null

  /**
   * Returns a plain object representing the currently dragged item. Every drag source must specify it by returning an object from
   * its beginDrag() method. Returns null if no item is being dragged.
   */
  getItem<T = DragObject>(): T

  /**
   * Returns a plain object representing the last recorded drop result. The drop targets may optionally specify it by returning an
   * object from their drop() methods. When a chain of drop() is dispatched for the nested targets, bottom up, any parent that explicitly
   * returns its own result from drop() overrides the drop result previously set by the child. Returns null if called outside drop().
   */
  getDropResult<T = DropResult>(): T | null

  /**
   *  Returns true if some drop target has handled the drop event, false otherwise. Even if a target did not return a drop result,
   * didDrop() returns true. Use it inside drop() to test whether any nested drop target has already handled the drop. Returns false
   * if called outside drop().
   */
  didDrop(): boolean

  /**
   * Returns the { x, y } client offset of the pointer at the time when the current drag operation has started. Returns null if no item
   * is being dragged.
   */
  getInitialClientOffset(): XYCoord | null

  /**
   * Returns the { x, y } client offset of the drag source component's root DOM node at the time when the current drag operation has started.
   * Returns null if no item is being dragged.
   */
  getInitialSourceClientOffset(): XYCoord | null

  /**
   * Returns the last recorded { x, y } client offset of the pointer while a drag operation is in progress. Returns null if no item is being dragged.
   */
  getClientOffset(): XYCoord | null

  /**
   * Returns the { x, y } difference between the last recorded client offset of the pointer and the client offset when current the drag operation has
   * started. Returns null if no item is being dragged.
   */
  getDifferenceFromInitialOffset(): XYCoord | null

  /**
   * Returns the projected { x, y } client offset of the drag source component's root DOM node, based on its position at the time when the current
   * drag operation has started, and the movement difference. Returns null if no item is being dragged.
   */
  getSourceClientOffset(): XYCoord | null
}

export interface DragLayerMonitor<DragObject = unknown> {
  /**
   * Returns true if a drag operation is in progress. Returns false otherwise.
   */
  isDragging(): boolean

  /**
   * Returns a string or a symbol identifying the type of the current dragged item.
   * Returns null if no item is being dragged.
   */
  getItemType(): Identifier | null

  /**
   * Returns a plain object representing the currently dragged item.
   * Every drag source must specify it by returning an object from its beginDrag() method.
   * Returns null if no item is being dragged.
   */
  getItem<T = DragObject>(): T

  /**
   * Returns the { x, y } client offset of the pointer at the time when the current drag operation has started.
   * Returns null if no item is being dragged.
   */
  getInitialClientOffset(): XYCoord | null

  /**
   * Returns the { x, y } client offset of the drag source component's root DOM node at the time when the current
   * drag operation has started. Returns null if no item is being dragged.
   */
  getInitialSourceClientOffset(): XYCoord | null

  /**
   * Returns the last recorded { x, y } client offset of the pointer while a drag operation is in progress.
   * Returns null if no item is being dragged.
   */
  getClientOffset(): XYCoord | null

  /**
   * Returns the { x, y } difference between the last recorded client offset of the pointer and the client
   * offset when current the drag operation has started. Returns null if no item is being dragged.
   */
  getDifferenceFromInitialOffset(): XYCoord | null

  /**
   * Returns the projected { x, y } client offset of the drag source component's root DOM node, based on its
   * position at the time when the current drag operation has started, and the movement difference.
   * Returns null if no item is being dragged.
   */
  getSourceClientOffset(): XYCoord | null
}
